Chamfering apparatus, a grinding wheel, and a chamfering method

ABSTRACT

A chamfering apparatus for chamfering an outer periphery of a disk-shaped substrate includes a grinding member having a circular hole inside thereof, wherein the hole has a diameter larger than an outer diameter of the substrate. An inner periphery of the grinding member forming the hole is a grinding surface and grinds the outer periphery of the substrate.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a chamfering apparatus, a grinding wheel, and a chamfering method for a glass substrate of a hard disk used with a magnetic head of a magneto resistance type or a giant magneto resistance type.

In a process of manufacturing a glass disk for a glass substrate of a magnetic recording medium (a hard disk) mounted on various types of magnetic recording apparatuses, chamfer machining is generally done on circular edges at the outer periphery of the glass substrate obtained by press molding, for example. Through the chamfering process at an outer periphery of the glass disk, the circular edges at the outer periphery are chamfered to have an inclination by removing the edges. The chamfering is conducted on the glass disk because the glass disk having a keen edge at the outer periphery is dangerous and mechanically fragile to chip readily. Regarding chamfer machining on a glass disk, Patent Document 1 (Japanese Unexamined Patent Application Publication No. H11-198012), for example, discloses a chamfering apparatus and a chamfering method. The Patent Document 1 shows that the chamfer apparatus and method disclosed therein alleviate the load and shock generated in the chamfer process by setting the circumferential speed of the glass disk and the circumferential speed of the grinding wheel within respective appropriate ranges. Also, Patent Document 1 shows that a good chamfered surface can be attained by making the rotating direction of the grinding wheel and the rotating direction of the glass disk be the same.

In the apparatus and method of chamfering a glass disk disclosed in Patent Document 1, chamfering is conducted by making the outer periphery of the grinding wheel having a disk shape in contact with the outer periphery of the glass disk. FIG. 4 shows an arrangement in a chamfering process in which the outer periphery of the disk-shaped grinding wheel is made contact with the outer periphery of the glass disk. For chamfering the outer periphery of the glass disk 101, generally, the outer periphery of the rotating disk-shaped grinding wheel 102 is made into contact with the circular edge at the periphery of the rotating glass disk 101. Grinding fluid is supplied at a contact point, and the grinding wheel is pressed against the glass disk to grind the circular edge. The glass disk 101 is mounted on a base and chucked. The glass disk on the base rotates together with rotation of the base.

Some of commonly used glass substrates have an outer diameter of about 65 mm. In the course of chamfering on such a glass substrate, a grinding wheel with an outer diameter of about 160 mm is employed. Rotation speed of the grinding wheel is generally set in the range from 2,000 to 2,500 rpm for the chamfer machining. Depending on conditions in the chamfering process, so-called chipping, any broken chips (pieces or fragments) generated on the glass disk, may occur.

In the chamfer machining conducted by means of the outer periphery of the grinding wheel, the surface area at the contact point between the glass disk and the grinding wheel is relatively small. Consequently, the pressure acting on the outer periphery of the glass disk is high, which causes large load on the glass disk. At locations where the disk receives large load, chips may occur. In addition, some micro cracks may occur, thereby decreasing strength of the substrate.

In order to avoid this chipping, it can be considered to control a cutting speed in the chamfering process low and conduct careful machining. However, such a way of chamfering suppresses a high-speed fabrication of the glass substrate.

Moreover, the chamfer machining using the outer periphery of the grinding wheel causes a collision between the glass disk and the grinding wheel at the moment of contact therebetween. The glass disk is held on a rotatable base in the chamfer machining. A positioning of the glass disk, however, unavoidably accompanies some errors with respect to the predetermined location on the base. This causes an oscillation of the glass disk during the chamfer machining and frequent, quick collisions in proportion to the rotational speed of the grinding wheel. In the event of collision, the pressure on the glass disk from the grinding wheel rises abruptly. Repeating such collisions many times, the load on the glass disk further increases and the glass substrate tends to generate the chips.

In view of the above situation, it is an object of the present invention to provide a chamfering apparatus, a grinding wheel, and a chamfering method in which an occurrence of chipping is suppressed and the time for manufacturing a substrate is shortened.

Further objects and advantages of the invention will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION

A chamfering apparatus of the invention that chamfers circular edges at an outer periphery of a disk-shaped substrate comprises a grinding member having a circular hole inside thereof, the hole having a diameter larger than an outer diameter of the substrate. An inner peripheral surface of the grinding member forming the hole serves as a grinding surface that comes in contact with the circular edges of the substrate and grinds the circular edges.

In the chamfer machining using this chamfering apparatus, the center of curvature of the outer periphery of the substrate and the center of curvature of the inner periphery of the grinding member locate in the same side with respect to the contact point. That is, the outer peripheral surface of the substrate and the inner peripheral surface of the grinding member have respective curved surfaces that are curved towards the same direction. As a result, the surface area of the contact point between the substrate and the grinding member is relatively large due to a microscopic elastic deformation during the chamfer machining. Further, a pulling angle or rake angle of the substrate material by the grinding member is smaller in the chamfering apparatus of the invention, which has the centers of curvature of both of the substrate and the grinding member in the same direction, than in the conventional apparatus of FIG. 4, which has the centers of curvature in the opposite directions. Therefore, the load on the substrate is diffused, and generation of chips and micro cracks is suppressed. Since the load on the substrate is reduced, the chips and micro cracks are scarcely generated even at a raised cutting speed for the substrate. Hence, it has become able to raise cutting speed in the chamfer machining yet suppressing the occurrence of chipping. A higher cutting speed in the chamfer machining shortens the time for a chamfer step, and the time for manufacturing a substrate.

The grinding member of the invention chamfers the circular edges at the periphery of the disk-shaped substrate in which the grinding member comes in contact with the circular edges at an outer periphery of the substrate and grinds the circular edges to chamfer the substrate, and has a hole with a diameter larger than a diameter of the substrate inside the grinding member. The inner periphery of the grinding member around the hole serves as a grinding surface that comes in contact with the circular edges of the substrate and grinds the circular edges.

In a chamfering method according to the invention, the chamfering apparatus chamfers circular edges at the outer periphery of the disk-shaped substrate using the grinding member having the hole with the diameter larger than that of the substrate inside the grinding member. The chamfering is carried out by making the grinding member in contact with the circular edges of the substrate at the inner peripheral surface of the grinding member and grinding the circular edges of the substrate.

The present invention suppresses the occurrence of chipping and provides a substrate with an improved quality. In addition, the invention shortens the time for manufacturing the substrate and enhances productivity thereof.

Now, some preferred embodiments according to the invention will be described with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a chamfering apparatus according to an embodiment of the invention;

FIG. 2 is a sectional view taken along line 2-2 in the chamfering apparatus of FIG. 1;

FIGS. 3( a), 3(b), and 3(c) illustrate the contact point between a glass substrate and an inner periphery of the grinding wheel; and

FIG. 4 is a plan view of a chamfering apparatus of prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic plan view of a chamfering apparatus for a glass substrate of one embodiment according to the present invention. FIG. 2 is a sectional view taken along the line 2-2 in FIG. 1.

The chamfering apparatus 1 of this embodiment comprises a grinding wheel 2, which is a grinding member having a machining surface at the inner peripheral surface thereof, and a base 3 for attaching a work piece, which is a glass substrate 4 to be chamfered.

The grinding wheel 2 is a disk having a grinding wheel hole formed in the central region thereof. A machining surface is formed at the inner peripheral surface 6 of the grinding hole, the surface 6 forming the grinding wheel hole. The outer diameter of the grinding wheel 2 in this embodiment is 160 mm and the diameter of the inner peripheral surface 6 of the grinding wheel is 100 mm, the surface 6 forming the grinding wheel hole in the central region of the grinding wheel. The inner peripheral surface 6 of the grinding wheel is of a diameter larger than the outer diameter of the glass substrate 4, allowing the glass substrate 4 to be arranged inside the grinding wheel hole. A recess 9 is formed in the inner peripheral surface 6 of the grinding wheel 2 so that the glass substrate 4 comes in contact obliquely in the chamfering process. The recess 9 has a bottom plane 9 a, an upper machining plane 9 b, and a lower machining plane 9 c. The bottom plane 9 a is perpendicular to the record plane of the glass substrate 4 in which information is written. (The record plane is parallel to the horizontal plane in this embodiment, for example.) The upper machining plane 9 b and the lower machining plane 9 c become in contact with the upper and lower circular edges, respectively, of the glass substrate 4 obliquely with respect to the record plane. The inner peripheral surface 6 forming the grinding wheel hole in the grinding wheel 2 serves as a grinding surface that becomes in contact with the circular edges of the glass substrate 4 and grinds them. In the grinding wheel 2 of this embodiment, grinding particles of diamond are held on the surface of the grinding wheel having the grinding wheel hole and then an electroless plating of nickel is plated on the surface to fix the grinding particles of diamond on the grinding wheel. Roughness of the surface is of a grain size #325. The material for the grinding wheel is not limited to that of this embodiment described above, but other appropriate materials can be used.

The glass substrate 4 is preliminarily formed to a disk configuration by press molding, for example, and a central part is removed by coring process, for example, to form a toroidal shape. The glass substrate 4 has a glass substrate hole, and the inner periphery 7 of the glass substrate forms a glass substrate hole. The glass substrate 4 in this embodiment has an outer diameter of 65 mm and a circular glass substrate hole with an outer diameter of 20 mm formed by the inner periphery of the glass substrate. The glass substrate obtained in the press molding step remains having an outer peripheral shape that is almost the same as the shape of the die used in the press molding step, leaving circular edges at the outer periphery. Accordingly, the chamfering process is generally conducted to eliminate the circular edges on the glass substrate.

The base 3 is a support member to mount and support the glass substrate 4, so that the glass substrate 4 is chucked and fixed on the base 3. The chucking of the glass substrate 4 is carried out by pushing the glass substrate 4 down onto the base 3 with a pressing member 5 and by suction from bottom with the base 3. The pressing member 5 is formed in a hollow cylinder configuration and pushes the glass substrate 4 from above on the region from a radius of about 25 mm to a radius of 30 mm towards the base 3. The suction of the glass substrate 4 with the base 3 is carried out by drawing through a negative pressure set up in grooves 8 formed on the support surface of the base 3. The base 3 has three concentric grooves 8 that have a suction hole, respectively (not shown in the figure). The suction holes are connected to a tank (not shown in the figure) at the negative pressure through inside of the base 3. The tank is connected to a suction pump and a motor to drive the pump, which create the negative pressure in the tank preliminarily. This system produces the negative pressure in the grooves 8 to attract the glass substrate 4. Thus, the glass substrate 4 is fixed on the base 3 by pushing down onto the base 3 and attracting from bottom. The base 3 rotates with the glass substrate 4 chucked thereon to rotate the glass substrate 4 on the base 3.

Description has been made for a method for chucking the glass substrate 4 in this embodiment in which the glass substrate 4 is pushed down from above onto the base and yet attracted from bottom to the base. However, the method for chucking the glass substrate on the base 3 is not limited to the above-described method but other methods can be applied.

Next, a process for chamfering the glass substrate 4 with the grinding wheel 2 is described as follows.

A chamfering apparatus 1 of this embodiment allows disposing a glass substrate 4 inside the grinding wheel hole. The inner peripheral surface 6 forming the grinding wheel hole in the grinding wheel serves as a grinding surface that becomes in contact with the circular edges of the glass substrate to grind them. First, in the chamfering process, the glass substrate 4 is fixed and chucked on the base 3. After chucking the glass substrate 4, the base 3 with the glass substrate disposed thereon is rotated to rotate the glass substrate 4. The glass substrate 4 rotates together with the base 3 at a rotating speed in a range of 30 to 240 rpm. The grinding wheel 2 surrounding the glass substrate 4 rotates in the reversed direction to the rotation direction of the glass substrate as indicated by the arrows in FIG. 1. The grinding wheel 2 is set to rotate at a rotating speed of about 2,000 to 2,500 rpm.

In this embodiment, the glass substrate 4 is disposed inside the grinding wheel hole formed by the inner peripheral surface 6 of the grinding wheel 2 and chamfered at the contact point between the glass substrate 4 and the grinding wheel 2. Thus, the glass substrate 4 comes in contact with the grinding wheel at the inner peripheral surface 6 of the grinding wheel 2. Hence, the center of curvature of the outer periphery of the glass substrate 4 and the center of curvature of the inner periphery of the grinding wheel 2 locate at the same side with respect to the contact point. The outer periphery of the glass substrate 4 and the grinding wheel 2 also have curved surfaces facing the same direction. In these conditions of the embodiment, the contact surface area at the contact point between the grinding wheel 2 and the glass substrate 4 in the actual chamfering process is larger than that in a case in which chamfering is done by the outer peripheral surface of a grinding wheel as in the prior art. According to the pure geometry, the contact would occur at a single point similar to the case of chamfering at the outer peripheral surface of the grinding wheel in the prior art. Actually, however, the contact surface area in the process of chamfering the glass substrate 4 by the grinding wheel 2 is larger in the configuration of the invention. As a result, the pressing force per unit area acting between the glass substrate 4 and the grinding wheel 2 is reduced, thereby keeping the load on the glass substrate 4 at a relatively low level in the chamfering process.

The following describes the process to become contact and depart from the contact between the glass substrate 4 and the grinding wheel 2. FIGS. 3( a), 3(b), and 3(c) are enlarged views for illustrating the contact point between the glass substrate 4 and the grinding wheel 2. The structures other than the glass substrate 4 and the grinding wheel 2 are eliminated in FIGS. 3( a), 3(b), and 3(c) to simplify the illustration. FIG. 3( a) is a sectional view illustrating a state before the contact of the glass substrate 4 to the grinding wheel 2. As shown in FIG. 3( a), the glass substrate 4 is not chamfered yet and the outer periphery is in a configuration as-formed in the press molding step, with the circular edges remaining. From this state, the glass substrate 4 and the grinding wheel 2 are pushed against each other to chamfer the substrate.

Then, as shown in FIG. 3( b), the glass substrate 4 enters into the recess 9 of the inner peripheral surface of the grinding wheel 2, in which the circular edges of the glass substrate 4 come in contact with the upper machining plane 9 b and the lower machining plane 9 c that are parts of the recess 9. Since the upper machining plane 9 b and the lower machining plane 9 c of the recess 9 are oblique to the recording surface of the glass substrate 4, the upper and lower machining planes 9 b and 9 c come into contact with the circular edges obliquely, allowing to chamfer the edges. Thus, the upper and lower machining planes 9 b and 9 c, which are portions of the inner peripheral surface 6 of the grinding wheel, come into contact with the circular edges of the glass substrate 4 serving as grinding planes. After completion of the chamfer machining, the glass substrate 4 is separated from the grinding wheel 2 as shown in FIG. 3( c).

The contacting step in the chamfering process in this embodiment is performed gently between the glass substrate 4 and the inner peripheral surface 6 of the grinding wheel 2. The grinding place 10 in FIG. 1 refers to a plane at which chamfer machining is carried out by pushing the glass substrate 4 to the grinding wheel 2. The grinding place 10, which is a contact point between the glass substrate 4 and the grinding wheel 2, has a certain finite area, because the glass substrate 4 and the inner peripheral surface 6 have curved surfaces bending towards the same direction. Even if the glass substrate begins to contact on the inner peripheral surface 6 with a small misalignment with respect to the grinding place 10, during the course of movement of each contact point from each starting point of the edges towards the grinding point 10 accompanying an increase in contact area, the pressure between the glass substrate 4 and the grinding wheel 2 gradually increases. When the contact point between the glass substrate 4 and the grinding wheel 2 meets the grinding point 10, a chamfer machining process proceeds there. At the end of the chamfering process, the contact point between the glass substrate 4 and the grinding wheel 2 moves, decreasing the contact area, to the position at which the glass substrate 4 and the inner peripheral surface 6 of the grinding wheel 2 depart from the grinding place 10. Finally, the glass substrate 4 and the grinding wheel 2 become apart. During the departing process, the pressure acting between the two members gradually decreases.

When the glass substrate 4 comes into contact with inner peripheral surface 6 of the grinding wheel at a correct position without misalignment with respect to the grinding place 10, the contact area between the glass substrate 4 and the inner peripheral surface 6 of the grinding wheel gradually increases from the start of contact by a mutual pushing force, forming the grinding place 10. Since the grinding point 10 has a certain finite area, during the course from the start of the contact between the glass substrate 4 and the inner peripheral surface 6 of the grinding wheel to the formation of the grinding place 10, the pressure between the two members gradually increases. When the glass substrate 4 moves away from the inner peripheral surface 6 of the grinding wheel at the correct position without misalignment with respect to the grinding place 10, the contact area between the two members gradually shrinks and the pressure between them gradually decreases, and finally, the glass substrate 4 and the inner peripheral surface 6 of the grinding wheel become apart. Thus, the process of the contact and departure between the glass substrate 4 and the grinding wheel 2 proceeds with gentle increase and decrease of the pressure between the two members. Therefore, an abrupt change of the load on the glass substrate 4 from the grinding wheel 2 is avoided.

Since the load on the glass substrate 4 is reduced and the abrupt change of the load is avoided in the chamfering process as described above, a chipping scarcely occurs with a chamfering apparatus 1 and a grinding wheel 2 of the invention. Consequently, the chipping hardly occurs even when the rotating speed of the base 3 is raised to increase the rotating speed of the glass substrate 4 and the pushing force of the glass substrate onto the inner peripheral surface 6 of the grinding wheel is increased. As a result, the cutting speed in the chamfering process can be raised.

The cutting speed in the chamfer machining of this embodiment is set at about 10 mm/min. Since the cutting speed set in the conventional chamfer machining, in which the glass substrate is made in contact with the outer peripheral surface of the grinding wheel, is in the range from 0.1 to 0.5 mm/min, the chamfer machining is performed at a significantly higher speed in the embodiment than in the prior art technology. Therefore, the time for chamfering process is shortened.

When the glass substrate 4 is chucked on the base 3, it is still difficult in the embodiment of the present invention to exactly match the rotation center of the base 3 and the center of the glass substrate 4. It is very likely to generate some misalignment between the two centers. When there is a misalignment between the centers, the glass substrate 4 rotates with a lateral oscillation relative to the base 3 and comes into contact with the grinding wheel every time the glass substrate 4 rotates in the early stage of the chamfer process. Thus, collisions between the glass substrate 4 and the grinding wheel 2 are repeated.

Nevertheless, after the chamfer machining has proceeded passing over such misalignment between the center of the glass substrate 4 and the rotation center of the base 3 that caused the lateral oscillation, the oscillation relative to the grinding wheel 2 ceases and the glass substrate 4 continues in contact with the grinding wheel 2. Since the chipping scarcely occurs in an embodiment of the invention, the cutting speed of the glass substrate 4 by the grinding wheel 2 can be increased in the chamfer machining. At an elevated cutting speed, the chamfer machining proceeds rather quickly passing over the extent due to the misalignment. Hence, the repeated collision of the glass substrate against the grinding wheel can be reduced, suppressing the occurrence of chipping. Since the oscillation of the glass substrate 4 relative to the grinding wheel 2 is reduced, the occurrence of chipping can be further alleviated. As a result, the cutting speed of the glass substrate 4 by the grinding wheel 2 can be further increased.

The following describes experimental results demonstrating a decrease in the chip generation in the chamfer apparatus according to the embodiment of the invention. Table 1 shows rates of occurrence of the chipping at various rotating speeds when compared between the chamfering at the inner peripheral surface of a grinding wheel according to the present invention and the chamfering at the outer peripheral surface of a grinding wheel according to a prior art.

TABLE 1 Rotating speed 240 120 60 30 of the base 3 (rpm) Rate of occurrence of 100 100 90 70 chipping (%) in chamfering of a prior art Rate of occurrence of 10 5 0 0 chipping (%) in chamfering of the invention

Conditions in the experiments are as follows.

In the chamfering at the inner peripheral surface of the grinding wheel according to the invention, the glass substrate had an outer diameter of about 65 mm, and had a circular hole with a diameter of 20 mm in the central region of the substrate. The grinding wheel, used in the chamfer machining at the inner peripheral surface thereof according to the invention, had an outer diameter of 160 mm and had a hole with a diameter of 100 mm in the central region of the grinding wheel, the hole being formed by the inner peripheral surface of the grinding wheel. In the grinding wheel used in the experiments, as in the embodiment described above, grinding particles of diamond were fixed on the surface of the grinding wheel having a hole and electroless nickel plating was plated thereon to fix the grinding particles of diamond on the grinding wheel surface. The roughness of the surface was of a grain size of #325.

In these experiments, for chamfering at the inner periphery of a grinding wheel according to the invention, the chamfering apparatus of the embodiment example as described above was used. For chamfering at the outer periphery of a grinding wheel according to a prior art, a grinding wheel used in the experiments had an outer diameter of 160 mm, had no grinding wheel hole, and had a machining surface at the outer periphery. Glass substrates used in the experiments are the same as in the chamfering in the above-described embodiment example.

The experiments were executed only for the purpose of studying a trend of chip generation. Therefore, the grinding wheel was held stationary and not rotated. The rotating glass substrate was made in contact at various rotating speed with the held grinding wheel. The glass substrate was observed after the chamfering to inspect the occurrence of chipping. The observation on the glass substrate was carried out by an optical microscope that was capable of measuring the size of the generated chips. The occurrence of chip generation was defined by the observation of chips having the size larger than 200 μm. When the glass substrate was made in contact with the grinding wheel, the center of the glass substrate was positioned with an eccentricity of 50 μm with respect to the center of rotation of the base. The cutting speed in the chamfer machining was set at 10 mm/min in these experiments.

As shown in Table 1, the chamfer machining at the outer peripheral surface of the grinding wheel according to the prior art resulted in the chip generation with high rates over the whole rotating speed rages of 30 to 240 rpm. At the rotating speeds of 120 rpm and 240 rpm, in particular, the chipping occurred at the rate of 100%. In contrast, the chamfer machining at the inner peripheral surface of the grinding wheel according to the invention demonstrated generally low rates of chip generation. At the rotating speeds of 30 rpm and 60 rpm, in particular, no chip was generated, that is, the rate of occurrence of chipping was zero.

Thus, the chamfering according to the invention, in which the contact between the glass substrate and the grinding wheel takes place at the inner peripheral surface of the grinding wheel, showed much lower rates of the occurrence of the chipping than the chamfering in the prior art, in which the contact between the glass substrate and the grinding wheel takes place at the outer peripheral surface of the grinding wheel. Hence, a high quality of a glass substrate after chamfer machining is obtained. Since the chipping scarcely occur at a high rotating speed of the base in the chamfering process of the invention, in which the contact between the glass substrate and the grinding wheel takes place at the inner peripheral surface of the grinding wheel, it is possible to raise the rotating speed of the base and increase the mutual pushing force between the glass substrate and the grinding wheel. Consequently, the cutting speed can be raised to shorten the time for the chamfering process.

Sizes and configuration of the glass substrate and the grinding wheel are not limited to those of the embodiment examples. Rather, every element constituting a substrate and a chamfering apparatus can have any other size and configuration as long as the chamfer machining is carried out at the inner peripheral surface of the grinding wheel.

The disclosure of Japanese Patent Application No. 2007-157603, filed on Jun. 14, 2007, is incorporated in the application.

While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims. 

1. A chamfering apparatus for chamfering an outer periphery of a disk-shaped substrate, comprising: a grinding member having a circular hole inside thereof, the hole having a diameter larger than an outer diameter of the substrate to receive the substrate therein, and a grinding surface at an inner periphery thereof to chamfer the outer periphery of the substrate.
 2. A chamfering apparatus according to claim 1, wherein said grinding member includes, as the grinding surface, a recess provided along the inner periphery and having an upper machining plane and a lower machining plane with a vertical plane therebetween, the upper and lower machining planes being arranged obliquely with respect to the substrate to form upper and lower peripheral edges of the substrate, respectively.
 3. A chamfering apparatus according to claim 1, further comprising: a base member provided inside the hole for placing the substrate thereon and rotating the substrate, and a pressing member provided inside the hole for sandwiching the substrate between the pressing member and the base member.
 4. A chamfering apparatus according to claim 3, further comprising grooves provided on the base member, and suction holes provided in the grooves and adapted to be connected to a suction pump for applying a negative pressure to the substrate to firmly attract the substrate to the base member.
 5. A chamfering apparatus according to claim 4, further comprising first means for rotating the base member in one direction, and second means for rotating the grinding member in a direction opposite to the one direction.
 6. A grinder for grinding a disk-shaped substrate to chamfer an outer periphery of the substrate, wherein the grinder has an annular shape with a hole therein, said hole having a diameter larger than an outer diameter of the substrate and being defined by an inner periphery, said inner periphery having a recess extending along the same to serve as a grinding surface contacting the substrate.
 7. A grinder according to claim 6, wherein said grinding surface comprises an upper machining plane and a lower machining plane with a vertical plane therebetween, provided in the recess, the upper and lower machining planes being arranged obliquely with respect to the substrate so that the upper and lower machining planes contact an upper and lower peripheral edges of the substrate for chamfering, respectively.
 8. A method of chamfering an outer periphery of a disk-shaped substrate, comprising: preparing a grinding member having a circular hole inside thereof, the hole having a diameter larger than an outer diameter of the substrate and being defined by an inner periphery, arranging the substrate in the hole to contact the inner periphery of the grinding member to chamfer the substrate, and rotating the grinding member and the substrate.
 9. A method of chamfering according to claim 8, wherein the grinding member has a groove with a grinding surface to chamfer the substrate.
 10. A method of chamfering according to claim 8, wherein said grinding member is rotated in one direction, and the substrate disposed on a base member is rotated in a direction opposite to the one direction. 